1. Field of the Invention
The present invention relates to an organic electroluminescence display device, and more particularly to an organic electroluminescence display device which can prevent picture quality deterioration due to the characteristic deterioration of transistors provided in respective pixels.
2. Description of the Prior Art
Currently, the use of a liquid crystal display (LCD), which is a display device that is in replacement of a CRT, is gradually increasing. Since the LCD is not a self-luminous display, it requires a separate light source, and this causes power consumption to be heightened and thinning of the LCD to be limited. Additionally, since the LCD obtains an image signal by the reaction of the liquid crystal, the display of a high-speed moving image is limited due to response time of the liquid crystal. Also, its viewing angle is limited. As described above, an organic electroluminescence display device has been developed as a display device that is in replacement of the LCD. This organic electroluminescence display device uses the phenomenon of light emission of an organic or polymeric material when an electric field is applied to the organic or polymeric material.
Hereinafter, an organic electroluminescence display device will be explained with reference to FIG. 1.
FIG. 1 is a block diagram illustrating the construction of an organic electroluminescence display device.
The organic electroluminescence display device is provided with a panel 11, a gate driver 12 and a data driver 13 connected to the panel 11, and a timing control unit 14 for controlling the panel 11, the gate driver 12 and the data driver 13. The panel 11 includes a plurality of gate lines G1, G2, . . . , Gm-1 and Gm arranged in parallel and a plurality of data lines D1, D2, Dn-1 and Dn arranged to cross the gate lines G1, G2, . . . , Gm-1 and Gm. In areas surrounded by the gate lines G1, G2, . . . , Gm-1 and Gm and the data lines D1, D2, Dn-1 and Dn, which are in the form of a matrix, respectively, unit pixels are formed.
FIG. 2 is a circuit diagram illustrating each pixel of a conventional organic electroluminescence display device.
Referring to FIG. 2, each pixel of the conventional organic electroluminescence display device is provided with a switching transistor T1, a capacitor C, a driving transistor T2 and an organic LED OLED1.
The drain terminal of the switching transistor T1 is connected to a data line D, and its gate terminal is connected to a gate line G. The switching transistor T1 is turned on/off by the gate signal transferred to the gate line G. If the transistor T1 is turned on, it transfers a data signal from the data line D to the capacitor C and the driving transistor T2. The capacitor C is connected to a power line P for supplying an external voltage, and maintains the data signal for one frame. The gate terminal of the driving transistor T2 is connected to the source terminal of the switching transistor T1 and the capacitor C, and its drain terminal is connected to the power line P. The driving transistor T2 is turned on/off by the data signal applied from the switching transistor T1 and the data signal charged in the capacitor C, i.e., by the data signal on a common connection terminal of the switching transistor T1 and the capacitor C. If the driving transistor T2 is turned on by the data signal, it adjusts the amount of current flowing through the power line P and transfers the adjusted current to the organic LED OLED1. As a result, the organic LED OLED1 irradiates light in proportion to the amount of current i1 transferred to the organic LED. Here, the anode of the organic LED OLED1 is connected to the source terminal of the driving transistor T2 and the cathode terminal of the organic LED OLED1 is connected to the ground terminal GND.
In the conventional organic electroluminescence display device, if the pixel is turned on by the gate signal, the driving transistor T2 provided in the pixel is turned on for a frame by the data signal on the common connection terminal of the switching transistor T1 and the capacitor C, and continuously applies the current i1 to the organic LED OLED1. Accordingly, the characteristic of the driving transistor T2 deteriorates to cause the threshold voltage Vth of the driving transistor T2 to be changed. If the output current of the driving transistor T2 is changed due to the change of the threshold voltage Vth, the uniformity and luminance of light irradiated by the organic LED OLED1 are degraded to cause the picture quality deterioration, and the lifespan of the organic LED OLED1 is shortened to cause the lifespan of the organic electroluminescence display device also to be shortened.